Ever since Freeza its basicly been Super Saiyan this, Super Saiyan that. If you're not able to turn into a green eyes, blonde haired badass you got no bussiness in fighting whoever the next badguys are.
Picolo can sort of trail along, but even he cannot keep up.

i'm now watching the Buu saga, Yamcha quit fighting, Tien quit fighting, Chiautzu quit fighting, Krilin is painfully aware of his uselessness but just tags along out of curiosity. Picolo is the only non-SS to even try, and without much success.

Its kinda my biggest issue with the series. Its still enoyable to watch, but it rapidly makes a whole cast of imo interesting characters redundant and demotes them to the role of comicrelief or filler.

I feel like I'm the only one who isn't all that bothered by the human's decrease of attention in DBZ. I like Krillin and Tien, but that's about it. All of the other humans introduced in DB were just kinda meh to me.

DBZ made up for shoving the humans in the background by introducing Vegeta.